[NSRCA-discussion] JR Servos of choice these days

Wed Jan 7 21:24:39 AKST 2009

Ihncheol,

I don't know if the 3400G and the 3517 are truly the same servo.  The 3517
is listed for airplane and heli use.  I don't see the 3400G currently
listed, and I don't recall what it was recommended for.  My only reservation
about using the 3400G would be the "G" designation, which is for gyro.  The
G servos often have higher gain settings (good for heli tailrotors and
gyros) which when used on airplanes are great for a very accurate and
aggressive center, but can contribute to jittering.  There are several JR
servos that have identical dimensions, weight, speed, and torque, but
different model numbers and different narrative applications.  The majority
of the time, it is the exact same servo, but the gain is tailored to a
specific application.

Regards,

Dave

  _____  

From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Ihncheol Park
Sent: Wednesday, January 07, 2009 2:58 PM
To: General pattern discussion
Subject: Re: [NSRCA-discussion] JR Servos of choice these days

Dave,

Isn't the JRPS3517 a relabeled JRPS3400G ??

Identical specifications except 3400 never came out with MG.

I'm going to try 3400Gs on Elevators since they show same spec with 3517
unless Horizon doesn't recommand it?  

Ihncheol

  _____  

From: Dave <DaveL322 at comcast.net>
To: General pattern discussion <nsrca-discussion at lists.nsrca.org>
Sent: Wednesday, January 7, 2009 12:10:45 PM
Subject: Re: [NSRCA-discussion] JR Servos of choice these days

Ok....here goes...

My "standard" servo package for many years has been: 
9411sa on ailerons 
8411sa on rudder 
8417sa on elevator 
3421sa on throttle (better yet, Castle 85 HV <G>) 

As FYI for those not familiar with JR servo nomenclature - 
- DS prefix indicates digital. 
- MG indicates metal gear. 
- SA indicates metal and nylon geartrain (generally metal pinion on servo
motor, with metal output shaft, and 2 or 3 intermediate gears are nylon). 
- 4 digit number indicates coreless motor. 
- 3 digit number indicated cored motor (3 or 5 pole). 
- 1st number indicates general case size (ie, 8411 and 821 share same
mounting pattern). 
There are some exceptions, but the above is applicable to most current and
past JR servos. 

Speed and torque generally increase proportionately to increased voltage,
and I have always run relatively high voltage to improve servo performance.
In my glow days, I used 5 cell unregulated Nicd or Nimh to power the
receiver and servos, and "bump" charged every couple flights to keep the
battery voltage high.  When I converted to electric powerplants, I started
using (in parallel) 2 sets of TP 2s1p480 lipos regulated to 6.53 volts
through Tech-Aero Vregs. 

8417 - is only available as a MG servo.  The 8417sa is an 8417 that has had
the 3 intermediate metal gears replaced with the nylon gears from an 8411sa
or 8231 (buy the 8231 gearset, it is all nylon, and costs less).  8231 gear
ratio is slightly slower than the 8417, so an 8417sa at 6.5 volt is about
0.09 sec and 130 oz/in torque. 

9411 - I don't know of a midsize JR servo better suited for ailerons (save
running 6.5 volts instead of 6 volts, which is good for about 0.01 sec on
that servo). 

3421 - I've used this servo a lot (including pairs mounted horizontally on
the engine mount for the Webra 160MC), but never in pairs on elevator as I
prefer a single servo.  However, the 3421sa is a good choice (in pairs) for
elevator @ .015 sec and 75 oz/in torque @ 6v.  The 3517 is another option -
slightly faster (and less torque) - 0.09 sec and 51 oz/in torque @ 6v.

8411 - this servo is close to 200 oz/in @ 6.5v.  Several years ago, I ran
the 8411sa and 8611 back to back in my EMC, and I couldn't tell the
difference between them in flight, so I've stayed with the 8411 as it is
lighter (and the rudder size has not increased on the majority of planes
since that time - but the fuses have!). 

Brief sidenote about metal / nylon gears.  Metal gears are for strength
(especially when space is at a premium), but are typically manufactured with
small clearances (slop) to avoid binding.  Nylon gears can have zero
clearance without binding (gears flex instead) have better wear properties.
I find the nylon gears ever so slightly more accurate for very fine control
inputs ("leaning" on the stick, without actually moving the stick).
However, the nylon stuff will deflect ever so slightly under load, whereas
the metal gears do not flex under, so the "personality" of the servos at
center and just off center can be slightly different.  Linkages/control
surfaces with any flex or slop will hide 99% of the differences in
comparable servos.  And, typically, all metal gear servos will weigh about
.1 - .3 oz more.

Regards,

Dave 

-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Jon Lowe
Sent: Wednesday, January 07, 2009 8:56 AM
To: nsrca-discussion at lists.nsrca.org
Subject: Re: [NSRCA-discussion] JR Servos of choice these days

9411SA's (mid-size) on aileron, 8611a on rudder, 3421sa's on elevator 
(or my new choice, 3421's with the JRPSG3025 gear set middle two gears. 
Much faster, and plenty of torque, particularly on 6+ volts.  On 
throttle, I use a servo mounted sideways (output shaft horizontal) 
directly on the engine mount,  Hitec HS-56HB.  Very tight and fast.  I 
change the throttle servos out after a year of use.

I hope Dave Lockhart chimes in here.  I'd like to find a faster 
alternative to the 9411sa's in the same size package.

Jon Lowe

-----Original Message-----
From: Woodward, Jim (US SSA) <jim.woodward at baesystems.com>
To: NSRCA-discussion <nsrca-discussion at lists.nsrca.org>
Sent: Wed, 7 Jan 2009 7:19 am
Subject: [NSRCA-discussion] JR Servos of choice these days

Guys,

I?m finishing a pattern plane for a friend.  He needs
to know what the choice of JR servos are these days.  I need two 
aileron servo
choices, 1 rudder servo, 2 elevator mini digitals, and a mini for the
throttle.  Any recommendations would be great.

Thanks,

Jim W.

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